Abstract

Fiber reinforced composite materials are materials are increasingly being used in many applications. Composite materials go through a complex process of material state changes (e.g. distributed damage development, accumulation, and interaction) which affect global property (strength and stiffness) degradation and eventual failure. Despite significant progress, different modes of local changes are often difficult to characterize and estimation of remaining properties can be quite challenging. The objective of this paper is to enhance understanding of local mechanisms and property evolution to facilitate design for damage tolerance and durability. For this purpose, a new material state description is provided based on the understanding that microstructural degradation causes heterogeneous charge polarization inside composite materials. This frequency dependent dielectric response measured using broadband dielectric spectroscopy (BbDS) provides important features which directly relate to degradation behavior and associated loss of properties (strength and stiffness). In this study, material state change has been discussed in two example cases: i) Damage distribution and remaining property (strength and stiffness) after low velocity impact until barely visible impact damage (BVID) limit, and ii) Evolution of damage mechanisms in different laminates during tension loading. A 3D X-ray microscope has been used to visualize and hence validate evolution of damage. Validated results from these test cases show that degradation process, and evolution of properties can be represented by material state variables with a high sensitivity. Relationship of property degradation (mechanical and dielectric) with modes of damage evolution has been discussed at the fundamental level. This provides an opportunity for the development of predictive modeling which of interest in aerospace and other applications. Details of experimental methods and results will be included in the paper.